/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet.http;

import java.util.Enumeration;
import javax.servlet.ServletContext;

/**
 * 
 * Provides a way to identify a user across more than one page request or visit
 * to a Web site and to store information about that user.
 * 
 * <p>
 * The servlet container uses this interface to create a session between an HTTP
 * client and an HTTP server. The session persists for a specified time period,
 * across more than one connection or page request from the user. A session
 * usually corresponds to one user, who may visit a site many times. The server
 * can maintain a session in many ways such as using cookies or rewriting URLs.
 * 
 * <p>
 * This interface allows servlets to
 * <ul>
 * <li>View and manipulate information about a session, such as the session
 * identifier, creation time, and last accessed time
 * <li>Bind objects to sessions, allowing user information to persist across
 * multiple user connections
 * </ul>
 * 
 * <p>
 * When an application stores an object in or removes an object from a session,
 * the session checks whether the object implements
 * {@link HttpSessionBindingListener}. If it does, the servlet notifies the
 * object that it has been bound to or unbound from the session. Notifications
 * are sent after the binding methods complete. For session that are invalidated
 * or expire, notifications are sent after the session has been invalidated or
 * expired.
 * 
 * <p>
 * When container migrates a session between VMs in a distributed container
 * setting, all session attributes implementing the
 * {@link HttpSessionActivationListener} interface are notified.
 * 
 * <p>
 * A servlet should be able to handle cases in which the client does not choose
 * to join a session, such as when cookies are intentionally turned off. Until
 * the client joins the session, <code>isNew</code> returns <code>true</code>.
 * If the client chooses not to join the session, <code>getSession</code> will
 * return a different session on each request, and <code>isNew</code> will
 * always return <code>true</code>.
 * 
 * <p>
 * Session information is scoped only to the current web application (
 * <code>ServletContext</code>), so information stored in one context will not
 * be directly visible in another.
 * 
 * @author Various
 * @version $Version$
 * 
 * 
 * @see HttpSessionBindingListener
 * @see HttpSessionContext
 * 
 */

public interface HttpSession {

	/**
	 * 
	 * Returns the time when this session was created, measured in milliseconds
	 * since midnight January 1, 1970 GMT.
	 * 
	 * @return a <code>long</code> specifying when this session was created,
	 *         expressed in milliseconds since 1/1/1970 GMT
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public long getCreationTime();

	/**
	 * 
	 * Returns a string containing the unique identifier assigned to this
	 * session. The identifier is assigned by the servlet container and is
	 * implementation dependent.
	 * 
	 * @return a string specifying the identifier assigned to this session
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public String getId();

	/**
	 * 
	 * Returns the last time the client sent a request associated with this
	 * session, as the number of milliseconds since midnight January 1, 1970
	 * GMT, and marked by the time the container received the request.
	 * 
	 * <p>
	 * Actions that your application takes, such as getting or setting a value
	 * associated with the session, do not affect the access time.
	 * 
	 * @return a <code>long</code> representing the last time the client sent a
	 *         request associated with this session, expressed in milliseconds
	 *         since 1/1/1970 GMT
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public long getLastAccessedTime();

	/**
	 * Returns the ServletContext to which this session belongs.
	 * 
	 * @return The ServletContext object for the web application
	 * @since 2.3
	 */

	public ServletContext getServletContext();

	/**
	 * 
	 * Specifies the time, in seconds, between client requests before the
	 * servlet container will invalidate this session. A negative time indicates
	 * the session should never timeout.
	 * 
	 * @param interval
	 *            An integer specifying the number of seconds
	 * 
	 */

	public void setMaxInactiveInterval(int interval);

	/**
	 * Returns the maximum time interval, in seconds, that the servlet container
	 * will keep this session open between client accesses. After this interval,
	 * the servlet container will invalidate the session. The maximum time
	 * interval can be set with the <code>setMaxInactiveInterval</code> method.
	 * A negative time indicates the session should never timeout.
	 * 
	 * 
	 * @return an integer specifying the number of seconds this session remains
	 *         open between client requests
	 * 
	 * @see #setMaxInactiveInterval
	 * 
	 * 
	 */

	public int getMaxInactiveInterval();

	/**
	 * 
	 * @deprecated As of Version 2.1, this method is deprecated and has no
	 *             replacement. It will be removed in a future version of the
	 *             Java Servlet API.
	 * 
	 */

	public HttpSessionContext getSessionContext();

	/**
	 * 
	 * Returns the object bound with the specified name in this session, or
	 * <code>null</code> if no object is bound under the name.
	 * 
	 * @param name
	 *            a string specifying the name of the object
	 * 
	 * @return the object with the specified name
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public Object getAttribute(String name);

	/**
	 * 
	 * @deprecated As of Version 2.2, this method is replaced by
	 *             {@link #getAttribute}.
	 * 
	 * @param name
	 *            a string specifying the name of the object
	 * 
	 * @return the object with the specified name
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public Object getValue(String name);

	/**
	 * 
	 * Returns an <code>Enumeration</code> of <code>String</code> objects
	 * containing the names of all the objects bound to this session.
	 * 
	 * @return an <code>Enumeration</code> of <code>String</code> objects
	 *         specifying the names of all the objects bound to this session
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public Enumeration getAttributeNames();

	/**
	 * 
	 * @deprecated As of Version 2.2, this method is replaced by
	 *             {@link #getAttributeNames}
	 * 
	 * @return an array of <code>String</code> objects specifying the names of
	 *         all the objects bound to this session
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public String[] getValueNames();

	/**
	 * Binds an object to this session, using the name specified. If an object
	 * of the same name is already bound to the session, the object is replaced.
	 * 
	 * <p>
	 * After this method executes, and if the new object implements
	 * <code>HttpSessionBindingListener</code>, the container calls
	 * <code>HttpSessionBindingListener.valueBound</code>. The container then
	 * notifies any <code>HttpSessionAttributeListener</code>s in the web
	 * application.
	 * 
	 * <p>
	 * If an object was already bound to this session of this name that
	 * implements <code>HttpSessionBindingListener</code>, its
	 * <code>HttpSessionBindingListener.valueUnbound</code> method is called.
	 * 
	 * <p>
	 * If the value passed in is null, this has the same effect as calling
	 * <code>removeAttribute()<code>.
	 * 
	 * 
	 * @param name
	 *            the name to which the object is bound; cannot be null
	 * 
	 * @param value
	 *            the object to be bound
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public void setAttribute(String name, Object value);

	/**
	 * 
	 * @deprecated As of Version 2.2, this method is replaced by
	 *             {@link #setAttribute}
	 * 
	 * @param name
	 *            the name to which the object is bound; cannot be null
	 * 
	 * @param value
	 *            the object to be bound; cannot be null
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 * 
	 */

	public void putValue(String name, Object value);

	/**
	 * 
	 * Removes the object bound with the specified name from this session. If
	 * the session does not have an object bound with the specified name, this
	 * method does nothing.
	 * 
	 * <p>
	 * After this method executes, and if the object implements
	 * <code>HttpSessionBindingListener</code>, the container calls
	 * <code>HttpSessionBindingListener.valueUnbound</code>. The container then
	 * notifies any <code>HttpSessionAttributeListener</code>s in the web
	 * application.
	 * 
	 * 
	 * 
	 * @param name
	 *            the name of the object to remove from this session
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 */

	public void removeAttribute(String name);

	/**
	 * 
	 * @deprecated As of Version 2.2, this method is replaced by
	 *             {@link #removeAttribute}
	 * 
	 * @param name
	 *            the name of the object to remove from this session
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an invalidated session
	 */

	public void removeValue(String name);

	/**
	 * 
	 * Invalidates this session then unbinds any objects bound to it.
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an already invalidated session
	 * 
	 */

	public void invalidate();

	/**
	 * 
	 * Returns <code>true</code> if the client does not yet know about the
	 * session or if the client chooses not to join the session. For example, if
	 * the server used only cookie-based sessions, and the client had disabled
	 * the use of cookies, then a session would be new on each request.
	 * 
	 * @return <code>true</code> if the server has created a session, but the
	 *         client has not yet joined
	 * 
	 * @exception IllegalStateException
	 *                if this method is called on an already invalidated session
	 * 
	 */

	public boolean isNew();

}
